360 REICHLE, DINGER, EDWARDS, HARRIS, AND SOLLINS 



ECOSYSTEM ANALYSIS 

 Forest Carbon Budget 



Although data may exist in great detail for parts of the ecosystem, synthesis 

 is necessary before the behavior of the entire system can be described. The 

 annual carbon budget for the ecosystem is one way of examining productivity 

 and energy flow in the forest. In a budget the system is divided into storage 

 compartments connected by transfer pathways. Data must include both the 

 fluxes of carbon transferred along each pathway during the course of the year 

 and the amount by which each compartment level changes during the same time 

 period. Such budgets represent initial steps in the construction of dynamic 

 simulation models. 



Ecosystem carbon budgeting follows the principle of conservation of mass, 

 namely, AQ = El — EL, where AQ is the change in compartment level, Si is the 

 sum of all incomes to compartment Q, and SL is the sum of all losses. In the 

 carbon budget for the Liriodendron forest (Fig. 3), some values were calculated 

 by assuming conservation of mass and are appropriately indicated in Table 6. In 

 several cases, information concerning transfers could be derived by two 

 independent calculations. Thus translocation of carbon from leaves to lateral 

 roots was estimated by solving the mass-balance equation for the lateral-root 

 compartment and apportioning translocation among the leaf compartments in 

 proportion to their biomasses. The same fluxes were also evaluated by solving 

 each leaf-mass-balance equation for the carbon transfer out of leaves to lateral 

 roots. Both estimates are shown in Table 6. 



The Carbon Cycle 



Although concise and mathematically balanced, the matrix representation of 

 the forest carbon budget (Table 6) does not easily permit ecological interpreta- 

 tion; a pictorial form of the budget is presented in Fig. 3. Only photosynthetic 

 fixation, respiratory losses, and compartment carbon levels and increments are 

 shown. On the right-hand side, the metabolic parameters for the system have 

 been summarized. Gross primary production (GPP) was estimated at 1.51 kg C 

 m 2 year 1 , net primary production (NPP) was 0.685 kg C m 2 year 1 , and net 

 annual increment (annual change in compartment levels) of autotrophs was 0.17 

 kg C m year . Autotrophic respiration (Ra) of 0.941 kg C m year and 

 heterotrophic respiration (Rh) of 0.524 kg C m year sum for a total 

 ecosystem respiration (Re) of 1.330 kg C m 2 year 1 . Heterotrophic respiration 

 was 31% of Re and was almost entirely a consequence of decomposer activity. 

 Compartment carbon value (standing crop) for autotrophs was 8.66 kg C/m 2 of 

 which 19% (1.67 kg/m ) consisted of roots. Heterotrophic biomass was 

 estimated at 7.05 g C/m 2 , and detritus (including standing deadwood and litter) 

 amounted to 12.85 kg C/m 2 . 



